It seems to me as your husband needs assurance that its over. Since it has been over for years and you have no contact make sure your husband knows the truth nd that you made a mistake and let him know he can e-mail him or call him or do whateve since you have nothing to hide and if that makes him feel better and earn your trust again you dont mind. You just have to be sure you told him the truth and I feel after awhile your husband will top this behavior and trust you slowly gain you just hae to go along right now.He still loves you he is just having a hard time trusting you play along and when he IM"s him or whatever try not to feed into th argument and tell him I told you the truth about everything there is no more you can find out. Show him that it doesnt bother you that he is still investigating it will blow over once he realizes that you are honest which seems you are,hang in there and you know how to slowly seduce your husband back to you.Just think of the past and he will come back to you,right now he is hurt and maybe not sure you are honest.
Hope this helped you out